[Platform] Add provider-level record/replay cassettes for test mocks

[wachterjohannes]

Q	A
Bug fix?	no
New feature?	yes
Docs?	yes
Issues	-
License	MIT

Builds on / lands after #2123 (the Mock test provider). Sibling of #2128 (HTTP-boundary cassettes); both are independent and stack on #2123.

Adds a provider-level record/replay tool for tests that only need a realistic, deterministic answer from a provider — without a network or API key.

Symfony\AI\Platform\Mock\Recording\RecordingProvider decorates a real ProviderInterface. By default the mode follows the cassette file:

• Record — when the cassette file does not exist yet: invokes the real provider, serializes its finished ResultInterface into a JSON Cassette, and returns it.
• Replay — when the cassette exists: rebuilds the result from the cassette and returns it; the real provider is never called, so it can be built with a placeholder key.

Delete the cassette to re-record. The mode can be forced via the record constructor argument (e.g. record: false in CI to fail loudly instead of issuing a real request when a cassette is missing).

use Symfony\AI\Platform\Bridge\Anthropic\Factory;
use Symfony\AI\Platform\Mock\Recording\Cassette;
use Symfony\AI\Platform\Mock\Recording\RecordingProvider;

$provider = new RecordingProvider(
    Factory::createProvider($_SERVER['ANTHROPIC_API_KEY'] ?? 'no-key-needed-on-replay'),
    new Cassette(__DIR__.'/fixtures/weather.json'),
);

$result = $provider->invoke('claude-3-7-sonnet-latest', $messages);

ResultSerializer supports text, structured output (ObjectResult), embeddings (VectorResult), tool calls (ToolCallResult) and text streams. Interactions are matched by a signature over (model, input, options) and consumed FIFO.

Scope note: on replay the recorded result is returned verbatim, so the bridge ResultConverter runs only at record time. To exercise bridge internals (converter/formatter) offline, use the HTTP-boundary cassette (Mock\Http\CassetteHttpClient, #2128) instead. Result metadata and token usage are not preserved in this first version.

Includes CHANGELOG entry, a docs subsection under Testing Tools, and offline tests (incl. an Anthropic record→replay demo). PHPUnit, PHPStan, php-cs-fixer and doctor-rst are green.

[OskarStark]

You should check Symfony repo there is an open pull request for cassettes like this IIRC

[wachterjohannes]

You should check Symfony repo there is an open pull request for cassettes like this IIRC

@OskarStark you mean symfony/symfony#63781 (RecorderHttpClient, php‑vcr‑style HAR record/replay)? Good catch. That one records at the HTTP boundary, so it overlaps with the sibling #2128, not this PR.

This RecordingProvider sits a layer higher: it records the already‑converted ResultInterface returned by a ProviderInterface, so it's bridge‑agnostic, needs no http-client, and on replay it skips the converter entirely. Different trade‑off, complementary to a HTTP‑level recorder. I'll add a note to the PR cross‑referencing #63781 so the layering is clear.